The present invention relates to a liquid crystal display apparatus whose power consumption is reduced.
In recent years, the power consumption of a liquid crystal display apparatus has been reduced by lowering the driving voltage or driving frequency. To further reduce the power consumption, a structure in which a memory is arranged for every pixel is proposed (Jpn. Pat. Appln. KOKAI Publication No. 58-196582 or 3-77922). With this technique employed for a still image, once display signals are transmitted to the respective pixels, the pixels may always be displayed with the signals held in the memories of the pixels. Theoretically, since only the power necessary for polarity inversion is consumed, the power consumption for the still image almost becomes "0".
However, along with the progress in multimedia, display of moving images has been increasingly required recently. In a moving image, image information sequentially changes at a high speed. For this reason, even memories are provided in units of pixels, signals held in the memories must be frequently rewritten. To frequently rewrite the held signals (pixel signals), a large power is consumed, as in prior arts.
In the above-described LCD with pixel memories, display signals obtained through switches SW are held in the pixel memories, and an image is displayed using the contents held in the memories. When this technique is to be applied to still image display, pixel signals are temporarily stored in the pixel memories. Unless the image changes, the memory contents need not be rewritten. Therefore, the driving frequency or static power consumption is expected to lower. However, for a moving image, the memory contents must be rewritten so no power consumption reduction effect can be expected, unlike still image display.
A demand has arisen for a low-power liquid crystal display apparatus capable of reducing the power consumption even in case of moving image display, and for portable equipment using the liquid crystal display apparatus as an image display device, minimizing waste of the battery, i.e., the main power supply of the equipment to prolong the battery driving time.